ENGR00233056 ALSA: adjust dma wm & buffersize configuration strategy

ENGR00233056 ALSA: adjust dma wm & buffersize configuration strategy

 Previously SSI/ESAI/SPDIF used one same-sized buffers and watermark(the
WM in the title) for every alsa driver.

 This patch allow each driver config its own buffer size and watermark,
which is obviously more flexible.

 Also, it sets SSI's buffersize from 256k to 64k.

Signed-off-by: Nicolin Chen <b42378@freescale.com>